Tension management devices for stented prosthesis delivery device

ABSTRACT

Delivery devices for delivering a stented prosthesis to a target site are disclosed. Disclosed delivery devices include a handle assembly including an actuator, an inner shaft assembly interconnected to the handle assembly, and are configured to releasably retain the stented prosthesis to the delivery device with at least one elongate tension member. The delivery devices further include a tension management device that is configured to limit the amount of tension that can be applied via the actuator to the at least one tension member. Certain embodiments are configured to apply different tension limits to different tension members that are controlled by a one or more actuators. Other various embodiments include one or more tension adjustors to selectively adjust one or more tension limits.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Non-Provisional Patent Application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 62/469,111, filed Mar. 9, 2017, the entire teachings of which are incorporated herein by reference.

BACKGROUND

This disclosure relates to delivery devices and tension management devices to control and limit the tension applied to at least one elongate tension member compressively retaining a stented prosthesis to the delivery device.

A human heart includes four heart valves that determine the pathway of blood flow through the heart: the mitral valve, the tricuspid valve, the aortic valve, and the pulmonary valve. The mitral and tricuspid valves are atrio-ventricular valves, which are between the atria and the ventricles, while the aortic and pulmonary valves are semilunar valves, which are in the arteries leaving the heart. Ideally, native leaflets of a heart valve move apart from each other when the valve is in an open position, and meet or “coapt” when the valve is in a closed position. Problems that may develop with valves include stenosis in which a valve does not open properly, and/or insufficiency or regurgitation in which a valve does not close properly. Stenosis and insufficiency may occur concomitantly in the same valve. The effects of valvular dysfunction vary, with regurgitation or backflow typically having relatively severe physiological consequences to the patient.

Diseased or otherwise deficient heart valves can be repaired or replaced using a variety of different types of heart valve surgeries. One conventional technique involves an open-heart surgical approach that is conducted under general anesthesia, during which the heart is stopped and blood flow is controlled by a heart-lung bypass machine.

More recently, minimally invasive approaches have been developed to facilitate catheter-based implantation of the valve prosthesis on the beating heart, intending to obviate the need for the use of classical sternotomy and cardiopulmonary bypass. In general terms, an expandable valve prosthesis is compressed about or within a catheter, inserted inside a body lumen of the patient, such as the femoral artery, and delivered to a desired location in the heart where the valve prosthesis is then deployed.

The disclosure presents improvements related to the above.

SUMMARY

The present disclosure relates to delivery devices for stented prosthesis loading, delivery and implantation. Such delivery devices can include an optional outer delivery sheath assembly, an inner shaft assembly and a handle assembly. The delivery devices provide a loaded delivery state in which the stented prosthesis is loaded and compressed over the inner shaft assembly. Compression of the stented prosthesis can be adjusted with one or more elongate tension members, e.g., sutures or the like, which extend around the stented prosthesis and proximately to an actuation and release assembly, which can, in some embodiments, be provided in the handle assembly. The delivery device can be manipulated to adjust tension in the tension members to permit the stented prosthesis to compress, self-expand, and ultimately release from the inner shaft assembly.

Disclosed embodiments further include a tension management device to maintain the necessary tension in one or more tension members (i.e. compression of the stented prosthesis) while also preventing the over tensioning of tension members to the point of damage or failure, which could compromise the procedure. In various embodiments, the tension management device is configured to limit the tension that can be applied to one or more tension members having differing predetermined tension limits. In further embodiments, the tension management device can adjust or toggle between varying tension limits for the one or more tension members. The disclosed embodiments result in a user friendly device that likely increases user confidence and is believed to reduce the risk associated with transcatheter stented prosthesis delivery procedures utilizing elongate tension members for retaining the stented prosthesis on the delivery device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example of a delivery device for delivering a stented prosthesis.

FIG. 2A is a schematic illustration of the delivery device of FIG. 1 having the stented prosthesis positioned over an inner shaft assembly of the delivery device in a compressed arrangement with a plurality of elongate tension members.

FIG. 2B is a schematic illustration of the delivery device of FIG. 2A having the stented prosthesis positioned over the inner shaft assembly of the delivery device in an expanded arrangement with the plurality of elongate tension members.

FIG. 3A is a perspective view of a stented prosthetic heart valve that can be used with the delivery devices disclosed herein shown in the expanded arrangement.

FIG. 3B is a front view of the stented prosthetic heart valve of FIG. 3A in the compressed arrangement.

FIG. 4 is a side view of one handle assembly having a tension management device that can be used with a delivery device, such as that of FIGS. 1-2B.

FIG. 5 is a perspective view of an actuator of the handle assembly of FIG. 4.

FIG. 6A is a partially exploded, first side view of a tension management device incorporated into the handle assembly of FIG. 4.

FIG. 6B is a partially exploded, second side view of the tension management device of FIG. 6A.

FIG. 6C is a partial top view of the assembled tension management device of FIGS. 4 and 6A-6B (a housing of the tension management device is shown as transparent for ease of illustration).

FIG. 6D is a partial side view of the assembled tension management device of FIGS. 4 and 6A-6C (the housing of the tension management device is shown as transparent for ease of illustration).

FIG. 7A is an enlarged view of select components of the tension management device of FIGS. 4 and 6A-6D illustrating a reel biased with a biasing element such that it engages a drive gear when tension in a respective tension member is below a predetermined limit.

FIG. 7B is an enlarged view of select components of the tension management device of FIGS. 4 and 6A-7A illustrating the reel disengaged with the drive gear, against the bias of the biasing element, when the tension in the respective tension member exceeds the predetermined limit.

FIG. 8A is a partial, side view of an alternate handle assembly having a tension management device including a toggle switch configured to adjust the predetermined tension limit of at least one tension member connected to a reel of the tension management device (a housing of the tension management device is shown as transparent for ease of illustration).

FIG. 8B is a partial, side view of the handle assembly of FIG. 8A showing the toggle switch in a first position (wherein the housing is shown as transparent for ease of illustration).

FIG. 8C is a partial, side view of the handle assembly of FIGS. 8A-8B showing the toggle switch in a second position (wherein the housing is shown as transparent for ease of illustration).

FIG. 9 is a top view of an alternate tension management device (having a housing shown as transparent for ease of illustration).

FIG. 10 is a side view of an alternate handle assembly having a tension management device that can be used with a delivery device, such as that of FIGS. 1-2B.

FIG. 11 is a partial, side view of an alternate actuator engaging a drive gear of the tension management device of FIG. 10 (a housing of the tension management device is shown as transparent for ease of illustration).

DETAILED DESCRIPTION

Specific embodiments of the present disclosure are now described with reference to the figures, wherein like reference numbers indicate identical or functionally similar elements.

As described below, aspects of the present disclosure relate to delivery devices utilizing one or more elongate tension members (e.g., sutures, chords, wires or filaments) to retain a stented prosthesis for delivery to a target site. By way of background, general components of one non-limiting example of a delivery device 10 with which some embodiments of the present disclosure are useful are illustrated in FIGS. 1-2B. The delivery device 10 is arranged and configured for percutaneously delivering a stented prosthesis. For example, the stented prosthesis can be a stented prosthetic heart valve 30 (schematically illustrated, hereinafter “prosthetic valve”). The delivery device 10 includes an optional outer sheath assembly 12 having an outer sheath 14, an inner shaft assembly 16 and a handle assembly 18. One or more elongate tension members 20 are provided, and can be considered part of the delivery device 10 in some embodiments or as part of the prosthetic valve 30 in other embodiments. The delivery device 10 provides a loaded, compressed arrangement (FIG. 2A) in which the prosthetic valve 30 is loaded over and is compressively retained on a spindle 22 of the inner shaft assembly 16 by the tension members 20. As is schematically illustrated in FIGS. 2A-2B, compression of the prosthetic valve 30 is adjustable by varying the tension in the one or more tension members 20. In this embodiment, the outer sheath 14 is interconnected to a capsule 24 that is selectively disposed over the compressed prosthetic valve 30 and assists in constraining the prosthetic valve 30. Once loaded, compressed and optionally sheathed by the capsule 24, the prosthetic valve 30 is delivered to the target site. When the prosthetic valve 30 is at the target site, the capsule 24 is withdrawn and tension in the tension members 20 is lessened or released to permit the prosthetic valve 30 to self-expand to an expanded arrangement, partially releasing and ultimately fully deploying the prosthetic valve 30 from the inner shaft assembly 16 (see, FIG. 2B). Movement of the outer sheath 14 and capsule 24 relative to the prosthetic valve 30 can be actuated by the handle assembly 18. The present disclosure focuses on numerous ways to incorporate a tension management device into a delivery device, such as the delivery device 10. As will be discussed in detail below, the disclosed tension management devices are arranged and configured to maintain and limit the tensioning force that can be transferred to the one or more tension members 20

As referred to herein, stented prostheses and stented prosthetic heart valves useful with the various devices and methods of the present disclosure may assume a wide variety of configurations, such as a bioprosthetic heart valve having tissue leaflets or a synthetic heart valve having polymeric, metallic or tissue-engineered leaflets, and can be specifically configured for replacing valves of the human heart. The stented prostheses and prosthetic valves of the present disclosure may be self-expandable, balloon expandable and/or mechanically expandable or combinations thereof. In general terms, the prosthetic valves of the present disclosure include a stent or stent frame having an internal lumen maintaining a valve structure (tissue or synthetic), with the stent frame having a normal, expanded condition or arrangement and collapsible to a compressed condition or arrangement for loading within the delivery device. For example, the stents or stent frames are support structures that comprise a number of struts or wire segments arranged relative to each other to provide a desired compressibility and strength to the prosthetic valve. The struts or wire segments are arranged such that they are capable of self-transitioning from, or being forced from, a compressed or collapsed arrangement to a normal, radially expanded arrangement. The struts or wire segments can be formed from a shape memory material, such as a nickel titanium alloy (e.g., Nitinol™). The stent frame can be laser-cut from a single piece of material, or can be assembled from a number of discrete components.

One non-limiting example of the stented prosthetic valve 30 is illustrated in detail in FIGS. 3A-3B. As a point of reference, the prosthetic valve 30 is shown in a normal or expanded arrangement in the view of FIG. 3A and a compressed arrangement in the view of FIG. 3B. The prosthetic valve 30 includes a stent or stent frame 32 and a valve structure 34. The stent frame 32 can assume any of the forms mentioned above, and is generally constructed to be self-expandable from the compressed arrangement to the normal, expanded arrangement. As discussed above, compression of the prosthetic valve 30 can be achieved with one or more tension members 20.

The valve structure 34 of the prosthetic valve 30 can assume a variety of forms, and can be formed, for example, from one or more biocompatible synthetic materials, synthetic polymers, autograft tissue, homograft tissue, xenograft tissue, or one or more other suitable materials. In some embodiments, the valve structure 34 can be formed, for example, from bovine, porcine, equine, ovine and/or other suitable animal tissues. In some embodiments, the valve structure 34 is formed, for example, from heart valve tissue, pericardium, and/or other suitable tissue. In some embodiments, the valve structure 34 can include or form one or more leaflets 36. For example, the valve structure 34 can be in the form of a tri-leaflet bovine pericardium valve, a bi-leaflet valve, or another suitable valve.

In some prosthetic valve constructions, such as that of FIGS. 3A-3B, the valve structure 34 can comprise two or three leaflets 36 that are fastened together at enlarged lateral end regions to form commissural joints, with the unattached edges forming coaptation edges of the valve structure 34. The leaflets 36 can be fastened to a skirt that in turn is attached to the stent frame 32. The prosthetic valve 30 includes a first end 40 and an opposing second end 44 of the prosthetic valve 30. As shown, the stent frame 32 can have a lattice or cell-like structure, and optionally forms or provides posts 46 corresponding with commissures of the valve structure 34 as well as features 48 (e.g., crowns, eyelets or other shapes) at the first and second ends 40, 44. If provided, the posts 46 are spaced equally around frame 32 (only one post 46 is clearly visible in FIG. 3A).

FIGS. 4-6D collectively illustrate components of an alternate handle assembly 118. The alternate handle assembly 118 can be incorporated into a delivery device, such as that of FIGS. 1-2B. The handle assembly 118 is configured and operates similarly to the handle assembly 18 except as explicitly stated. The handle assembly 118 of this embodiment includes an actuator 144 positioned over and engaged with one tension management device 150, which is connected to one or more tension members 120 positioned around a stented prosthesis as shown in FIGS. 1-2B, for example. The actuator 144 is configured to adjust tension in the tension members 120 via the tension management device 150, while the tension management device 150 further is configured to limit the amount of tensioning force that can be applied to the tension members 120. In one example embodiment, the actuator 144 translates rotational force of the actuator 144 to an actuator gear 156 of the tension management device 150 to selectively tension or release the tension in the tension members 120. In this example embodiment, the actuator 144 includes a generally cylindrical body 146 having a threaded interior surface 148. The tension management device 150 can include a housing 152, the actuator gear 156, a drive gear 158, a reel 160 and biasing element 162 (e.g., one or more pre-compressed springs, alternate resilient element or the like). Each of the actuator gear 156 and the drive gear 158 are positioned within the same plane and include a plurality of interlocking teeth 164, 166 (generally referenced). In this embodiment, the teeth 166 of the actuator gear 156 are angled with respect to a rotational axis of the actuator gear 156 to match the pitch of the threaded interior surface 148 of actuator 144. A few of the actuator gear teeth 164 are exposed with respect to an opening 154 in the housing 152 to enable engagement of actuator gear teeth 164 with the interior threaded surface 148 of the actuator 144. In this way, rotation of the actuator 144 in one direction (e.g., clockwise), subsequently rotates the actuator gear 156 about its axis, which correspondingly rotates the drive gear 158 about its axis. In conditions where the tension member tension limit is not met, the reel 160 is engaged with the drive gear 158 such that rotation of the drive gear 158 correspondingly rotates the reel 160. For example, one or more tension members 120 can be secured within a channel 170 of a reel 160 so that as the reel 160 rotates, the tension member(s) 120 are wound and unwound around the reel 160 to correspondingly compress and expand the prosthetic valve (not shown) as the tension in the tension member(s) 120 is varied. In embodiments where more than one elongate tension member is used to compresses the stented prosthesis, a plurality of tension members can individually be connected to one or more respective reels or a plurality of tension members can be secured to one elongate tension member that is connected to a reel.

The amount of tension that can be applied to compresses the stented prosthesis with the tension member(s) 120 (i.e. the tension limit) is dictated via the selection of the biasing element 162, which is positioned opposite the drive gear 158, between the reel 160 and the housing 152. The biasing element 162 biases the reel 160 in the direction of the drive gear 158 to urge at least one tooth 172 (referenced generally) of the reel 160 to engage one or more pockets 174 (referenced generally) in the drive gear 158 so that rotation of the drive gear 158 directly translates to rotation of the reel 160. As best shown in FIG. 6A, the drive gear 158 can optionally include a generally turbine-shaped face defining generally wedge-shaped pockets 174. The drive gear 158 and reel 160 interface can include, for example, four teeth 172 symmetrically positioned around the reel 160 that can respectively engage one of sixteen pockets 174 in the drive gear 158 to engage the reel 160. In one example embodiment, each tooth 172 has a generally triangular cross-section. The biasing element 162 is selected to provide a biasing force such that the reel 160 engages drive gear 158 in conditions where the tension in the tension member(s) 120 is under the predetermined limit but where the reel 160 slips and disengages the drive gear 158 in conditions where the tension meets or exceeds the predetermined limit due to compression of the biasing element 162. The displacement, or movement in which the teeth 172 of the reel 160 slip and disengage from the pockets 174 of the drive gear 158 can be about 1 mm, for example.

FIG. 6A illustrates the tension management device 150 in operating conditions where the tension applied to the elongate tension member(s) 120 is under the predetermined tension limit. In this condition, the teeth 172 of the reel 160 are engaged with pockets 174 of the drive gear 158. Once the maximum tension force is achieved, as shown in FIG. 6B, the biasing element 162 sufficiently compresses such that the reel teeth 172 disengage from the drive gear 158, against the bias of the biasing element 162 so that any rotation of the drive gear 158 is not transferred to the reel 160. In this condition, tension is maintained in the tension member(s) 120 but no additional force is applied by rotation of the drive gear 158 (i.e. even if the actuator 144 and actuator gear 156 continue to drive and rotate the drive gear 158). Therefore, when the biasing element 162 is disengaged from the drive gear 158, the reel 160 remains stationary and does not release tension in the at least one tension member 120. In certain embodiments, an audible click is provided once the reel 160 disengages the drive gear 158 to alert the user that the limit has been met. The audible click can be provided, for example, as a byproduct of the reel 160 slipping relative to the drive gear 158 due to the compression loaded on to the reel 160 during the slip of the reel 160 audibly clicks as it returns to the engaged state with the drive gear 158. In this configuration, the audible click continues during use as the reel 160 disengages and engages with the drive gear 158. In various embodiments, the tension is preselected, via selection of the biasing element 162, to limit the applied tension to a force of about 90 N to about 100 N, for example.

FIGS. 8A-8C illustrate an alternate handle assembly 118′, which is substantially similar to the handle assembly 118 disclosed above but further includes an optional tension limit adjuster 180 that can be incorporated into tension management devices 150, 250, 350 disclosed herein to adjust or select the tension limit of the tension management device. Tension adjuster 180 can be useful, for example, when different tension limits are desired during stented prosthesis loading and deployment procedures. For example, in one embodiment, tension adjuster 180 can function as a toggle switch for dictating the tension limit setting of the tension management device 150. In the illustrated embodiment, the tension adjuster 180 includes a two opposing tabs 182 that a user can grip to rotate the adjuster 180 in two positions (FIGS. 8B-8C). In each of the two positions, the adjuster 180 varies the compression of the biasing element 162, thus adjusting the bias on the reel 160, which correspondingly adjusts the maximum tension that can be transferred to the at least one tension member 120 connected to the respective reel 160. It is envisioned that other similar ways of varying the compression of the reel 160 are possible.

FIG. 9 illustrates an alternate tension management device 250 that is substantially similar to that of FIGS. 4 and 6A-7B. In this embodiment, the tension management device 250 includes a housing 252 (shown as partially transparent for clarity) having a window or opening 254. The tension management device 250 further includes an actuator gear 256 having at least some teeth 264 exposed with respect to the opening 254 to engage the associated actuator of the handle assembly (e.g., actuator 144 of FIGS. 4-5). The actuator gear teeth 264 are further engaged with the respective teeth 266 a, 266 b of two drive gears 258 a, 258 b. As with prior disclosed embodiments, each drive gear 258 a, 258 b is connected to a respective reel biased toward the respective drive gear 258 a, 258 b with a biasing element. In this configuration, at least two tension members 220 a, 220 b retain the stented prosthesis on the delivery device and are controllable via a single actuator (e.g., actuator 144). A first elongate tension member 220 a is interconnected to a first reel and a second elongate tension member 220 b is interconnected to a second reel. The first and second reels, as well as corresponding biasing elements, are positioned below the respective drive gears 258 a, 258 b and not visible in FIG. 9 but can be configured in the same way as the drive gear 158, reel 160 and biasing element 162 of FIGS. 7A-7B. In this embodiment, the tension members 220 a, 220 b are reeled in differing directions managed by opposing reel starting positions. Similar to the prior embodiments, during operating conditions where the tension applied to the tension members 220 a, 220 b is under the predetermined limit, each reel is engaged with the drive gear 258 a, 258 b via one or more respective teeth (e.g., teeth 172 of FIG. 7B). Once the maximum force is achieved, the respective reel disengages from the respective drive gear 258 a, 258 b such that the tension is maintained in the respective tension member(s) 220 a, 220 b, but no additional tensioning force is applied to the respective tension member(s) 220 a, 220 b even if the respective drive gear 258 a, 258 b continues to rotate (e.g., even if the actuator gear 256, via an actuator such as actuator 144, continues to drive one or more of the drive gears 258 a, 258 b). In some embodiments, the predetermined tension limit differs for the first and second reels, meaning that one reel can be engaged with the respective drive gear 258 a, 258 b when the second reel is not. As discussed above, the tension limit for each reel can differ by selecting the biasing element to provide the desired biasing force or by use of a tension adjuster to adjust the compression of the biasing element to provide the desired biasing force. In certain embodiments, an audible click, as described above, is provided once each reel disengages from the respective drive gear 258 a, 258 b to alert the user that the tension limit has been met. It is envisioned that more than two reels can be actuated by the actuator gear 256 in alternate embodiments. It is further envisioned that the delivery device can include one or more reels actuated by one or more respective actuators and/or one or more actuator gears connected to one or more respective actuators.

One alternate handle assembly 318 including an alternate tension management device 350 having an alternate actuator 344 is illustrated in FIGS. 10-11. In this embodiment, the actuator 344 includes a rotatable knob 356 fixed to a shaft 357 that extends through housing 352. The actuator gear of prior embodiments is omitted and the shaft 357 of the actuator 344 is directly connected to a drive gear 358. Rotation of the knob 356 in either the clockwise or counterclockwise direction applies corresponding 1:1 rotation of the shaft 357 and the drive gear 358, which subsequently rotates a corresponding reel 360, thus winding or unwinding tensioning member(s) 320 on the reel 360 to further tension or release tension in the tensioning member(s) 320, respectively. The reel 360 is biased toward the drive gear 358 with a biasing element 362, which functions as disclosed with respect to the biasing elements of prior embodiments. The actuator 344 can be incorporated into all embodiments disclosed herein, as desired.

Although the present disclosure has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A delivery device for delivering a stented prosthesis to a native heart valve; the delivery device comprising: a handle assembly including an actuator; an inner shaft assembly interconnected to the handle assembly and configured to releasably retain the stented prosthesis to the delivery device with at least one tension member, wherein tension in the tension member can be adjusted with the actuator; and a tension management device; wherein the tension management device is configured to limit the amount of tension that can be applied by the actuator to the at least one tension member wherein the tension management device includes a drive gear engageable with a reel, wherein the at least one tension member is connected to the reel such that the at least one tension member can be wound around the reel; further wherein the tension management device includes two drive gears, each drive gear connected to one respective reel.
 2. The delivery device of claim 1, wherein the tension management device includes an actuator gear engaged with the actuator.
 3. The delivery device of claim 1, wherein the tension management device includes a biasing element that biases the reel in a direction of the drive gear.
 4. The delivery device of claim 3, wherein the biasing element is a pre-compressed spring.
 5. The delivery device of claim 1, wherein an actuator gear translates rotation of the actuator to the drive gear.
 6. The delivery device of claim 5, wherein the actuator gear and the drive gear are positioned within the same plane.
 7. The delivery device of claim 1, wherein the reel includes a tooth that can engage the drive gear.
 8. The delivery device of claim 7, wherein the tooth has a generally triangular cross-section.
 9. The delivery device of claim 1, wherein the two drive gears are both actuated by a single actuating gear.
 10. The delivery device of claim 9, wherein the two drive gears can independently disengage from their respective reel.
 11. The delivery device of claim 1, wherein the actuator is directly connected to the drive gear.
 12. The delivery device of claim 1, wherein a limit in the amount of tension that can be applied to the at least one tension member is adjustable.
 13. The delivery device of claim 1, wherein an audible click is provided to inform a user that a maximum tensioning force has been achieved.
 14. The delivery device of claim 1, wherein the at least one tension member remains under tension when a maximum tensioning force has been achieved.
 15. The delivery device of claim 1, wherein the actuator is a rotatable knob.
 16. The delivery device of claim 1, wherein the at least one tension member includes a first tension member and a second tension member; wherein the inner shaft assembly is configured to releasably retain the stented prosthesis to the delivery device with the first tension member and the second tension member, wherein tension in the first and second tension members can be adjusted with the actuator; wherein the tension management device includes a first drive gear engageable with a first reel and a second drive gear engageable with a second reel, wherein a first tension member is connected to the first reel such that the first tension member can be wound around the first reel and wherein a second tension member is connected to the second reel such that the second tension member can be wound around the second reel.
 17. A delivery device for delivering a stented prosthesis to a native heart valve; the delivery device comprising: a handle assembly including an actuator; an inner shaft assembly interconnected to the handle assembly and configured to releasably retain the stented prosthesis to the delivery device with at least one tension member, wherein tension in the tension member can be adjusted with the actuator; and a tension management device; wherein the tension management device is configured to limit the amount of tension that can be applied by the actuator to the at least one tension member, wherein a limit in the amount of tension that can be applied to the at least one tension member is adjustable, further wherein the limit in the amount of tension that can be applied to the at least one tension member is adjustable with a toggle switch.
 18. The delivery device of claim 17, wherein the toggle switch adjusts compression of a biasing element.
 19. The delivery device of claim 17, wherein the tension management device includes a drive gear engageable with a reel, wherein the at least one tension member is connected to the reel such that the at least one tension member can be wound around the reel.
 20. The delivery device of claim 17, wherein the actuator includes a generally cylindrical body having a threaded inner surface.
 21. A delivery device for delivering a stented prosthesis to a native heart valve; the delivery device comprising: a handle assembly including an actuator; an inner shaft assembly interconnected to the handle assembly and configured to releasably retain the stented prosthesis to the delivery device with at least one tension member, wherein tension in the tension member can be adjusted with the actuator; and a tension management device; wherein the tension management device is configured to limit the amount of tension that can be applied by the actuator to the at least one tension member, wherein the actuator includes a generally cylindrical body having a threaded inner surface.
 22. The delivery device of claim 21, wherein the tension management device includes a drive gear engageable with a reel, wherein the at least one tension member is connected to the reel such that the at least one tension member can be wound around the reel. 